Spray painting is a painting technique where a device sprays a coating (paint, ink, varnish, etc.) through the air onto a surface. Spray guns evolved from airbrushes, and the two are usually distinguished by their size and the size of the spray pattern they produce. It is typically used for covering large surfaces with an even coating of liquid. Spray guns can be either automated or hand-held and have interchangeable heads to allow for different spray patterns. Single color aerosol paint cans are portable and easy to store.